Aye as long as some of the overpowered items from Equivalent Exchange are disabled, I do believe you can deny individual crafting recipes in the config files. Then it would be safe to open the server up to not being whitelisted.
Also if we could tie in the chat to the main server universe chat that'd be a good thing for the server. Main reason I think the tekkit server is suffering right now is because of it's isolation and well New PvP playing a part as well.
I enjoy Tekkit, I have to admit I have not visited the server in some time tho. So perhaps it has run it's course for now. But that's the thing about Tekkit, every update they make add something new or removes something from tekkit that changes the dynamic, which forces you to try it on again.
Tbh once Mojang and now the bukkit team absorbed by them continue their work on the Mod API, more blocks allowed etc. I believe the aim is 4096 blocks as opposed to the max 256 now. And the ongoing process of 1.3 and it's merging of single player and multiplayer, will enable Tekkit to be far more interesting with the likes of ThaumCraft 2 (excellent mod), Mo's Creatures etc. etc. being enabled for SMP play.
So I'm torn atm. If we can find another use for the server, that outshines Tekkit. I'd be all for it until Tekkit evolves a little more.